The present disclosure generally relates to a gas range system, and more particularly to enhancement of burner performance of a gas range system for a cooking appliance.
Conventional gas operated cooking appliances such as gas cooktops, for example, have one or more burners in which gas is mixed with air and burned. The burner will typically include an orifice and venturi assembly for the entrainment of air and for mixing the air with the gas required to generate the burner power output. The process of drawing air into the gas stream upstream of the burner assembly is referred to as “primary entrainment.” The gas is fed to the burner via a gas feed supply line that is connected to a suitable gas source. The flow of gas is mixed with the air in the venturi assembly to provide the primary aeration of the burner.
Generally, the gas coming out of the gas orifice has enough velocity and energy that when directed into the underside inlet of the gas burner it will induce surrounding air under the burner to be entrained with the gas stream into the burner. This is called “primary air” since it is prior to the combustion point or flame of the burner. For complete combustion of the gas (natural gas), approximately 9.4 parts of air is needed for every part of gas. If there is 100% primary air, all of the required 9.4 parts of air to go with the gas are present. (A 25000 Btu/hr burner with 100% primary air would have 0.416 cubic feet/min of gas and 3.91 cubic feet/min of primary air). If there is 143% primary air, there is 13.44 parts of air for every part of gas. At some point, if there is too much air, the mixture will be too lean and unable to start a flame.
In cases where a burner does not have 100% primary air, air comes in from outside the flame to supply the necessary air to complete the combustion. All residential burners are well below 100% primary air. The flames spread outward when a pot is placed over the flame because the flame has to work harder to find the secondary air it needs to completely combust the gas. With 100% primary air, the flames do not reach out around the pot because the flame already has all the air it needs.
The burner can also include burner ports that stabilize the flames for heating and cooking Additional air is entrained into the fuel downstream of the burner ports in what is referred to as “secondary entrainment.” The combination of the primary and secondary entrainment of air into the gas provides the reactants required for complete combustion of the gas delivered to the burner ports. Because such secondary entrainment occurs downstream of the burner ports, in a region in which cooking and handling activities take place, it is often desirable to limit the reliance on secondary entrainment. For higher capacity burners, it is desirable to boost the primary entrainment. One example of a system for boosting primary entrainment in a gas cooktop is described in U.S. patent application Ser. No. 10/814,722, filed on Mar. 31, 2004 and assigned to the assignee of the instant application, the disclosure of which is incorporated herein by reference in its entirety.
For gas burners, a turndown ratio is the ratio of the maximum output to the minimum output of the burner. Generally, the maximum output corresponds to the “power” or “speed” of the burner, while the minimum output corresponds to “simmer” capability of the burner. Because of the wide volumetric range associated with a high output burner, a larger turndown ratio, or a turbo burner, is most desirable for customers. A maximum output for such a high output burner will typically correspond to approximately 25,000 BTU/Hr, while a typical simmer rating is approximately 1,000 BTU/Hr. This results in a 25:1 turndown ratio, which is much higher than a typical BTU range, generally having turndown ratios of approximately 10:1. This wide range from the maximum output to the minimum output must also have a smooth transition.
To accomplish the range for a 25:1 turndown ratio, a stacked burner can be used. A stacked burner, also referred to as a vertically staged burner, generally uses two rings of gas outlets or ports, one over the other. One stage is used for simmer, while a combination of both stages can be used for power cooking One example of a dual stacked gas burner is described in U.S. Pat. No. 7,291,009, assigned to the assignee of the instant invention, the disclosure of which is incorporated herein by reference in its entirety. However, this stacked arrangement can create problems with controlling the gas flow to the appropriate burner and transitioning between burners while maintaining a prescribed, smooth output for the entire burner output range.
Generally in a stacked burner system, the simmer burner chamber can receive primary air from the primary air chamber of the main burner. Due to the relatively large diameter of the inlet into the main burner, the inlet into the simmer ring will dramatically skew the flow/flame distribution pattern around the simmer flame ports. It would be advantageous to be able to limit the skew of the flow/flame distribution pattern around the simmer flame ports.
A gas fuel boost pump may also be used to enhance a gas burner system in order to achieve a higher 25:1 turndown ratio. Traditional gas burners have very thin, uniform cross-section transition zones between the pre-combustion chamber and the flame port exit. In a gas fuel boost pump enhanced system, the high flow rates distributed through the main burner can create high turbulent intensity in these transition zones, where the mixture of primary air and the gas is not uniformly distributed. When combustion occurs in these zones, the white noise generated in these pockets can be significantly loud and may pose a perception problem with the consumer in the relatively quiet kitchen environment. It would be advantageous to be able to reduce the noise generated in these high turbulent intensity zones near the flame ports.
Where a gas fuel boost pump is used to increase the pressure of the gas flow received from the gas flow line, the gas flow must directly correlate with the gas valve stem and gas knob rotational position. This requires the ability to modulate the power to the gas fuel boost pump based on the knob position.
Traditional gas burners have burner ports that are generally configured to deliver a flame flow that is parallel to the cooking surface and the cooking utensil above the burner. This condition directly affects the efficiency of the burner to deliver heat to the cooking utensils. Gas burners are typically only 30-40% efficient. It would be advantageous to be able to increase the efficiency of a gas burner to deliver heat to the cooking utensil on the burner.
In a gas burner that provides an output of approximately 17,000-18,000 BTU/hr, the gas flow rate entering the venturi of the burner is in the range of approximately 2 to 2.5 cubic feet per minute (cfm). In order to increase the burner output, the input flow rate must also be increased. One way to do this while maintaining or increasing primary air entrainment is to increase the flow cross-sections. However, the amount of space that is available under the cooktop is limited. It would be advantageous to be able to increase the flow rate through the venturi despite the limited area under the cooktop. In addition, large flow cross-sections can be susceptible to the flame flashing back into the burner under low combustion simmer rates unless the primary air entering the burner is not sustainably increased to maintain port velocities above flame velocities associated with methane, natural gas, butane, and propane. It would be advantageous to balance a large flow area through the burner while maintaining a stable flame that does not flash back into the burner under low flow conditions.
Accordingly, it would be desirable to provide a system that addresses at least some of the problems identified above.